This invention relates to the blending of thermoplastic compositions having characteristics which are desireable but which have heretofor not been readily obtainable at a competitive cost.
Many organic liquids having a moderately low molecular weight are soluble in each other. When the molecular weight of an organic material is sufficiently great (macromolecular) to provide structural strength as a solid, such solid is generally not soluble in other macromolecular structural materials, (i.e. plastics). The compatibility and mutual solubility of organic plastics are generally not observed. Most attempts to mix pellets of different molding compositions at the time when the pellets are fed to an extruder result in extrudates having low strength by reason of the fracture lines at the boundaries amongst the different compositions. The discovery of a compatible blend of plastics, sometime referred to as plastic "alloys" is a significant and unexpected discovery by reason of the incompatibility of most of the conceivable permutations of mixtures of plastics.
Belgian Pat. No. 767,255 describes blends of polymethyl methacrylate and copolymers of styrene and maleic anhydride. DiGiulio U.S. Pat. No. 3,998,907 describes a method of preparing maleimide-containing copolymers by reacting amine or ammonia with particles of the copolymer comprising maleic anhydride under autogenous pressure at 125.degree. to 200.degree. C. Heretofor, copolymers of styrene and methyl methacrylate have been prepared, but such compositions have not had the combination of appropriate viscosity and softening temperatures desired in some operations.
Notwithstanding the persistent effort to prepare appropriate blends, there has been a failure by others to meet the demands for a blend having an attractive combination of adequate fluidity at molding temperatures, adequate stiffness in the molded product, and adequately high softening point.